On the question of detecting granulation signal in CoRoT light curves of A and B stars
We applied the procedure written by us to HgMn targets observed both through CoRoT astero and exo channels to check its usefulness for search of possible existence of solar-type granulation signature in their power spectrum. The point is that many articles appeared very recently considering this pro...
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irk-123456789-1194162017-06-07T03:04:19Z On the question of detecting granulation signal in CoRoT light curves of A and B stars Ghazaryan, S. We applied the procedure written by us to HgMn targets observed both through CoRoT astero and exo channels to check its usefulness for search of possible existence of solar-type granulation signature in their power spectrum. The point is that many articles appeared very recently considering this problem but, we did not find any paper on this issue in relation to chemically peculiar main-sequence stars. Because theoretical models based on atomic diffusion require that the atmospheres of ApBp stars have to be more stable than those of normal stars, presence or absence of granulation on their surfaces should be an interesting information for modelling. The earliest results show that our method is appropriate for analysis of data obtained through astero and exo channels. Nowadays, solar-type granulation effect most likely has not be seen within CoRoT data for the stars we considered. This issue needs further consideration. 2013 Article On the question of detecting granulation signal in CoRoT light curves of A and B stars / S. Ghazaryan // Advances in Astronomy and Space Physics. — 2013. — Т. 3., вип. 1. — С. 20-22. — Бібліогр.: 10 назв. — англ. 2227-1481 http://dspace.nbuv.gov.ua/handle/123456789/119416 en Advances in Astronomy and Space Physics Головна астрономічна обсерваторія НАН України |
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We applied the procedure written by us to HgMn targets observed both through CoRoT astero and exo channels to check its usefulness for search of possible existence of solar-type granulation signature in their power spectrum. The point is that many articles appeared very recently considering this problem but, we did not find any paper on this issue in relation to chemically peculiar main-sequence stars. Because theoretical models based on atomic diffusion require that the atmospheres of ApBp stars have to be more stable than those of normal stars, presence
or absence of granulation on their surfaces should be an interesting information for modelling. The earliest results show that our method is appropriate for analysis of data obtained through astero and exo channels. Nowadays, solar-type granulation effect most likely has not be seen within CoRoT data for the stars we considered. This issue needs further consideration. |
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Ghazaryan, S. |
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Ghazaryan, S. On the question of detecting granulation signal in CoRoT light curves of A and B stars Advances in Astronomy and Space Physics |
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Ghazaryan, S. |
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Ghazaryan, S. |
| title |
On the question of detecting granulation signal in CoRoT light curves of A and B stars |
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On the question of detecting granulation signal in CoRoT light curves of A and B stars |
| title_full |
On the question of detecting granulation signal in CoRoT light curves of A and B stars |
| title_fullStr |
On the question of detecting granulation signal in CoRoT light curves of A and B stars |
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On the question of detecting granulation signal in CoRoT light curves of A and B stars |
| title_sort |
on the question of detecting granulation signal in corot light curves of a and b stars |
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Головна астрономічна обсерваторія НАН України |
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2013 |
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http://dspace.nbuv.gov.ua/handle/123456789/119416 |
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On the question of detecting granulation signal in CoRoT light curves of A and B stars / S. Ghazaryan // Advances in Astronomy and Space Physics. — 2013. — Т. 3., вип. 1. — С. 20-22. — Бібліогр.: 10 назв. — англ. |
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Advances in Astronomy and Space Physics |
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AT ghazaryans onthequestionofdetectinggranulationsignalincorotlightcurvesofaandbstars |
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2025-07-08T15:50:21Z |
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On the question of detecting granulation signal
in CoRoT light curves of A and B stars
S.Ghazaryan∗
Advances in Astronomy and Space Physics, 3, 20-22 (2013)
© S.Ghazaryan, 2013
Byurakan Astrophysical Observatory, Aragatzotn Province, Byurakan, 0213, Armenia
LUTH, Observatoire de Paris, 5 Place Jule Janssen, 92190 Meudon, France
We applied the procedure written by us to HgMn targets observed both through CoRoT astero and exo channels
to check its usefulness for search of possible existence of solar-type granulation signature in their power spectrum.
The point is that many articles appeared very recently considering this problem but, we did not �nd any paper
on this issue in relation to chemically peculiar main-sequence stars. Because theoretical models based on atomic
di�usion require that the atmospheres of ApBp stars have to be more stable than those of normal stars, presence
or absence of granulation on their surfaces should be an interesting information for modelling. The earliest results
show that our method is appropriate for analysis of data obtained through astero and exo channels. Nowadays,
solar-type granulation e�ect most likely has not be seen within CoRoT data for the stars we considered. This issue
needs further consideration.
Key words: asteroseismology, HgMn stars, granulation
introduction
CoRoT (Convection, Rotation and Transits)1, a
satellite with 27 cm mirror, was successfully launched
on the 27th of December 2006. This instrument al-
lows to probe stellar interiors via variations of the
light curves which can be studied using the frequency
spectra. It provides a tool for deeper understand-
ing of internal structure of stars. Namely, if a large
number of modes penetrating to all possible depths
can be observed on the surface, than it is possi-
ble to �invert� the observations to make a map of
the sound speed throughout the star, and then to
deduce the temperature pro�le, with reasonable as-
sumptions about the chemical composition. Thus
asteroseismology lets us literally to see the interior
of stars because di�erent modes penetrate to di�er-
ent depths. With the data obtained through CoRoT
Astero channel we are able to study the modes more
carefully, to do frequency Fourier analysis which al-
lows us to have some idea about signature of solar
granulation e�ect in many stars. Granulation, as we
know, is a result of convection motions leading to
upward �ows of hotter plasma and downward �ows
of cooler plasma.
The discovery of global oscillations in the Sun by
Claverie et al. in 1979 [2] and Grec in 1980 [4] opened
a way for the new solar observations, for measur-
ing, for example, the depth of solar convection zone
and rotation of the Sun at di�erent depths and lat-
itudes. However, there is still a debate on the ques-
tion which type of oscillations can be hidden by stel-
lar granulation and the examination of solar gran-
ulation e�ect signature is not well done. Solar-like
oscillations have been detected from the ground in
radial velocity in several stars but because of high
uncertainties of the ground based observations it is
preferable to do high-precision photometry from the
space. In 2008 CoRoT team announced detection
of the solar-like oscillations and granulation in stars
hotter than the Sun. In the paper, published in Sci-
ence, they claim for the presence of these e�ects in
three main-sequence F-type stars (see [9] for more
details). The solar granulation frequency reaches up
to 2mHz for all of them. In 2010 Kallinger and
Matthews [6] announced possible existence of solar
granulation in early A-type stars. They presented
evidence for this e�ect in two δ Scuti stars of spec-
tral type A2: HD17493 and HD50844. That is why
we decided to search for signature of this e�ect also
in HgMn stars.
HgMn stars are the late B-type Chemically Pecu-
liar stars, the e�ective temperature of which is rang-
ing from 10 000K and 16 000K. They are character-
ized spectroscopically by large overabundances of Hg
(possibly up to 6 dex) and Mn (possibly up to 3 dex,
[1]). Overabundances greater than 2 dex of Be, Ga,
Y, Pt, Bi, Xe, Eu, Gd, W, and Pb are frequently
observed in these stars, while He, N, Mg, Al, Ni and
Zn often are underabundant by more than 0.5 dex
∗satenik.ghazaryan@obspm.fr
1The CoRoT space mission is developed and operated by the French Space Agency CNES, with participation of ESA's RSSD and
Science Programmes, Austria, Belgium, Brazil, Germany, and Spain.
20
Advances in Astronomy and Space Physics S.Ghazaryan
[10]. The elements C, O, Si, S, Ca, V, Cr and Fe
usually show only modest peculiarities, with abun-
dances within 0.5 dex of their solar one (classi�ed as
�normal type� elements in [10]). HgMn stars are slow
rotators, often binaries, and the existence of a weak
magnetic �eld in their atmospheres is still a subject
of debate. Because of their high e�ective temper-
atures, the HgMn stars should not host hydrogen
convective zones in their envelopes, and their low He
abundances may reduce the importance of He con-
vective zones as well. Such a quiet external layers al-
low atomic di�usion to proceed and hence to explain
the observed abundance anomalies [8]. The absence
of granulation in HgMn stars will give a new way to
prove the absence of convection zones in these stars
which is extremely important for understanding the
inner structure of these stars.
selected targets and analysis
The �rst step of analysis was to select a tar-
get which was observed by CoRoT Astero channel.
The selected target is HD175640 (the CoRoT ID is
7569). It was observed in 2008 during the SRc02,
which means that the observations were done during
the second Short Run to the Galaxy centre direc-
tion. This is a bright B9-type star with 6.21m ap-
parent magnitude and it belongs to the third Lumi-
nosity class targets. The light curve of CoRoT7569
is a combination of strong trends and weak jumps
(Fig. 1). The raw light curve of CoRoT7569, which
was obtained using our own procedure [3] written in
IDL language, does not show any transits (Fig. 2).
It is well detrended and there is no clear evidence
for granulation. To prove the absence of signature
of solar granulation in HgMn stars we calculated the
power spectrum of the light curve using Period04,
software written by Lenz and Breger in 2005 [7]. And
then, the same calculations were performed for the
original light curve. These two spectra are presented
in Fig. 3. The CoRoT orbital frequencies are also
overplotted on the graph.
To calculate the solar granulation frequency we
used the second equation given in [6]:
νgran ∝ νmax ∝ M ·R−2 · T−1/2
eff , (1)
where the mass, radius and e�ective temperature are
taken in solar units.
Assuming that
M/M� = 3.36, R/R� = 2.55,
Teff/Teff,� = 2.03, (2)
we mean that granulation frequency is νgran ∼
440µHz. As one can see from in Fig. 3 there are
no changes in the spectrum. It is almost �at which
means that there is no sign of granulation.
Fig. 1: Original light curve of CoRoT7569 obtained
through CoRoT Astero channel.
Fig. 2: Detrended light curve obtained through Colig-
Cor.
Fig. 3: Power spectra of the original and detrended
CoRoT7569 calculated with Period 04. The grey and
black curves correspond to the original and detrended
light curves, respectively. The frequencies marked below
the diagrams present the CoRoT orbital frequencies.
acknowledgement
I would like to express my gratitude to my super-
visors Georges Alecian and Hayk Harutyunyan for
their valuable directions and hearty guidance during
my PhD study.
21
Advances in Astronomy and Space Physics S.Ghazaryan
references
[1] AllerM.F. 1970, A&A, 6, 67
[2] ClaverieA., IsaakG.R., McLeodC.P., van der
RaayH.B. & CortesT.R. 1979, Nature, 282, 591
[3] Ghazaryan S.A., AlecianG. & HarutyunyanH.A. 2012,
in Fifty years of Cosmic Era: Real and Virtual Studies
of the Sky. Conference of Young Scientists of CIS Coun-
tries, 77
[4] GrecG., FossatE. & PomerantzM. 1980, Nature, 288,
541
[5] HeacoxW.D. 1979, ApJS, 41, 675
[6] KallingerT. & Matthews J.M. 2010, ApJ, 711, L35
[7] LenzP. & BregerM. 2005, Communications in Astero-
seismology, 146, 53
[8] MichaudG. 1970, ApJ, 160, 641
[9] Michel E., BaglinA., AuvergneM. et al. 2008, Science,
322, 558
[10] Takada-HidaiM. 1991, IAU Symposium, 145, 137
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